1. Field of the Invention
The present invention relates to an ink composition suitably used for inkjet recording, an inkjet recording method, and a printed material employing same; furthermore, it relates to a lithographic printing plate obtained using the ink, and a process for producing a lithographic printing plate. More particularly, it relates to an ink composition suitable for inkjet recording that cures with high sensitivity upon exposure to radiation, can form a high quality image, and has good storage stability, an inkjet recording method, a printed material employing same, a lithographic printing plate obtained using the ink, and a process for producing a lithographic printing plate.
2. Description of the Related Art
With regard to an image recording method for forming an image on a recording medium such as paper based on an image data signal, there are an electrophotographic system, sublimation type and melt type thermal transfer systems, an inkjet system, etc. In the electrophotographic system, a process of forming an electrostatic latent image on a photosensitive drum by electrically charging and exposing is required, and the system is complicated; as a result, there is the problem that the production cost is high. With regard to the thermal transfer system, although the equipment is inexpensive, due to the use of an ink ribbon there is the problem that the running cost is high and waste material is generated. On the other hand, with regard to the inkjet system, the equipment is inexpensive and, since an image is formed directly on a recording medium by discharging an ink only on a required image area, the ink can be used efficiently and the running cost is low. Furthermore, there is little noise and it is excellent as an image recording system.
An ink composition that can be cured by exposure to radiation such as ultraviolet rays and, in particular, an inkjet recording ink (radiation curing type inkjet recording ink) are required to have sufficiently high sensitivity and provide a high image quality. By achieving higher sensitivity, a large number of benefits are provided, such as high curability toward radiation, a reduction in power consumption, longer lifetime due to a decrease in the load on a radiation generator, and prevention of formation of low molecular weight material originating from insufficient curing. Furthermore, higher sensitivity particularly improves the cure strength of an image formed using the ink composition and, in particular, the inkjet recording ink, particularly for the formation of a lithographic printing plate, and high plate life can be obtained.
In recent years, the UV-curing inkjet system has been attracting attention since it has relatively low odor and can record on a recording medium that does not have rapid drying properties or ink absorbing properties. In particular, benzil, benzoin, benzoin ethyl ether, Michler's ketone, anthraquinone, acridine, phenazine, benzophenone, 2-ethylanthraquinone, etc. are generally used as photopolymerization initiators (ref. e.g. Bruce M. Monroe et al., Chemical Reviews, Vol. 93, p. 435-448 (1993)). However, when these photopolymerization initiators are used, since the curing sensitivity of a photopolymerizable composition is low, a long period of time is required for image exposure in the formation of an image. Because of this, in the case of a fine image, if there is slight vibration during operation, the image cannot be reproduced with good image quality and, moreover, since it is necessary to increase the amount of energy radiation from an exposure light source, it is necessary to take into consideration the radiation of a large amount of heat generated thereby.
JP-A-2004-91556 (JP-A denotes a Japanese unexamined patent application publication) proposes the combined use of an oxetane compound and a sensitizer for the purpose of providing an actinic radiation-curing composition and an actinic radiation-curing ink that enable very stable recording of a highly precise image, even under various printing environments, with excellent character quality and without the mingling of colors.